Discontinuous carbon dioxide release in the German cockroach, Blattella germanica (Dictyoptera: Blattellidae), and its effect on respiratory transpiration

The discontinuous gas exchange cycle (DGC) was described in the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae) for the first time. Also, the effect of the DGC on water loss was investigated. The CO2 emission pattern in both insecticide resistant and susceptible B. germanica varied with temperature. At 10, 15, and 20 °C the pattern was discontinuous. Cycle frequency increased at 25 and 30 °C, and at 35 °C the pattern became cyclic. In most DGCs, there was no clear distinction between the closed and flutter phases in both strains thus data for these phases were combined and analyzed as the interburst phase. The probability that B. germanica would breath discontinuously varied with temperature. Most cockroaches (62.8%) displayed DGCs at 10 °C, therefore measurement of metabolic rate and water loss was carried out at this temperature. Using repeated measures of analysis of variance, the interburst and burst V˙CO2(mlh-1) were not significantly different between the two strains. The variability in CO2 emission during the interburst and burst phases over time was not significantly different from cycle to cycle or between strains. Overall metabolic rate during the entire recording was not significantly different between both strains. There was a significant difference in the duration of the interburst and burst phases between the strains. The susceptible strain had significantly longer interburst and burst phase durations during a complete DGC than the resistant strain. The interburst and burst phase durations were 5.01±0.19 and 6.21±0.13min, respectively, for the resistant strain, whereas the durations were 7.16±0.37 and 6.73±0.17min, respectively, for the susceptible strain. This resulted in a DGC of significantly longer duration (13.89±0.44min) in the susceptible strain compared with the resistant strain (11.23±0.26min). The duration of the interburst phase was significantly different from the open phase duration in the resistant strain such that during a single DGC lasting ∼11.23min, 43.5% consisted of the interburst phase while the burst phase made up 56.5% of the cycle. The cuticular permeability at 10 °C and 0% RH was 2.26 μg cm−2 h−1 mmHg−1 for the resistant strain and 3.42 μg cm−2 h−1 mmHg−1 for the susceptible strain. In both strains, cuticular transpiration accounted for ∼95% of total water loss. The significantly longer duration of the interburst phase of the susceptible strain was not important in reducing water loss.